[PATCH 2/2] tracing/workqueue: separate singlethreaded workqueues

[Frederic Weisbecker <fweisbec@gmail.com>]

When a singlethread thread is added on the list, it is
appended to the first cpu workqueues. This is a mistake because
singlethreaded workqueues are not bounded to specific cpu but
on all online cpus.

On their cpu column, we will now find a * character.

# CPU  INSERTED  EXECUTED   NAME
# |      |         |          |

  *      0          0       kpsmoused
  *      0          0       ata_aux
  *      0          0       cqueue
  *      0          0       kacpi_notify
  *      0          0       kacpid
  *    998        998       khelper
  *      0          0       cpuset

  1      0          0       hda0/1
  1     42         42       reiserfs/1
  1      0          0       scsi_tgtd/1
  1      0          0       aio/1
  1      0          0       ata/1
  1    193        193       kblockd/1
  1      0          0       kintegrityd/1
  1      4          4       work_on_cpu/1
  1   1244       1244       events/1

  0      0          0       hda0/0
  0     63         63       reiserfs/0
  0      0          0       scsi_tgtd/0
  0      0          0       aio/0
  0      0          0       ata/0
  0    188        188       kblockd/0
  0      0          0       kintegrityd/0
  0     16         16       work_on_cpu/0
  0   1360       1360       events/0

Hmm, it looks like most of these workqueues are pointless :-)

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 include/trace/workqueue.h      |   16 +++--
 kernel/trace/trace_workqueue.c |  143 +++++++++++++++++++++++++++-------------
 kernel/workqueue.c             |   11 ++-
 3 files changed, 115 insertions(+), 55 deletions(-)

diff --git a/include/trace/workqueue.h b/include/trace/workqueue.h
index 867829d..4769c2d 100644
--- a/include/trace/workqueue.h
+++ b/include/trace/workqueue.h
@@ -5,13 +5,17 @@
 #include <linux/workqueue.h>
 #include <linux/sched.h>
 
+#define SINGLETHREAD_CPU	-1
+
 DECLARE_TRACE(workqueue_insertion,
-	   TPPROTO(struct task_struct *wq_thread, struct work_struct *work),
-	   TPARGS(wq_thread, work));
+	   TPPROTO(struct task_struct *wq_thread, struct work_struct *work,
+		   int singlethread),
+	   TPARGS(wq_thread, work, singlethread));
 
 DECLARE_TRACE(workqueue_execution,
-	   TPPROTO(struct task_struct *wq_thread, struct work_struct *work),
-	   TPARGS(wq_thread, work));
+	   TPPROTO(struct task_struct *wq_thread, struct work_struct *work,
+		   int singlethread),
+	   TPARGS(wq_thread, work, singlethread));
 
 /* Trace the creation of one workqueue thread on a cpu */
 DECLARE_TRACE(workqueue_creation,
@@ -19,7 +23,7 @@ DECLARE_TRACE(workqueue_creation,
 	   TPARGS(wq_thread, cpu));
 
 DECLARE_TRACE(workqueue_destruction,
-	   TPPROTO(struct task_struct *wq_thread),
-	   TPARGS(wq_thread));
+	   TPPROTO(struct task_struct *wq_thread, int singlethread),
+	   TPARGS(wq_thread, singlethread));
 
 #endif /* __TRACE_WORKQUEUE_H */
diff --git a/kernel/trace/trace_workqueue.c b/kernel/trace/trace_workqueue.c
index 4664990..38a1291 100644
--- a/kernel/trace/trace_workqueue.c
+++ b/kernel/trace/trace_workqueue.c
@@ -12,7 +12,6 @@
 #include "trace_stat.h"
 #include "trace.h"
 
-
 /* A cpu workqueue thread */
 struct cpu_workqueue_stats {
 	struct list_head            list;
@@ -41,18 +40,28 @@ struct workqueue_global_stats {
 static DEFINE_PER_CPU(struct workqueue_global_stats, all_workqueue_stat);
 #define workqueue_cpu_stat(cpu) (&per_cpu(all_workqueue_stat, cpu))
 
+static struct workqueue_global_stats singlethread_stat;
+
+
 /* Insertion of a work */
 static void
 probe_workqueue_insertion(struct task_struct *wq_thread,
-			  struct work_struct *work)
+			  struct work_struct *work, int singlethread)
 {
-	int cpu = cpumask_first(&wq_thread->cpus_allowed);
+	struct workqueue_global_stats *stats;
 	struct cpu_workqueue_stats *node, *next;
 	unsigned long flags;
+	int cpu;
+
+	if (singlethread)
+		stats = &singlethread_stat;
+	else {
+		cpu = cpumask_first(&wq_thread->cpus_allowed);
+		stats = workqueue_cpu_stat(cpu);
+	}
 
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-	list_for_each_entry_safe(node, next, &workqueue_cpu_stat(cpu)->list,
-							list) {
+	spin_lock_irqsave(&stats->lock, flags);
+	list_for_each_entry_safe(node, next, &stats->list, list) {
 		if (node->pid == wq_thread->pid) {
 			atomic_inc(&node->inserted);
 			goto found;
@@ -60,21 +69,28 @@ probe_workqueue_insertion(struct task_struct *wq_thread,
 	}
 	pr_debug("trace_workqueue: entry not found\n");
 found:
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
+	spin_unlock_irqrestore(&stats->lock, flags);
 }
 
 /* Execution of a work */
 static void
 probe_workqueue_execution(struct task_struct *wq_thread,
-			  struct work_struct *work)
+			  struct work_struct *work, int singlethread)
 {
-	int cpu = cpumask_first(&wq_thread->cpus_allowed);
 	struct cpu_workqueue_stats *node, *next;
+	struct workqueue_global_stats *stats;
 	unsigned long flags;
+	int cpu;
+
+	if (singlethread)
+		stats = &singlethread_stat;
+	else {
+		cpu = cpumask_first(&wq_thread->cpus_allowed);
+		stats = workqueue_cpu_stat(cpu);
+	}
 
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-	list_for_each_entry_safe(node, next, &workqueue_cpu_stat(cpu)->list,
-							list) {
+	spin_lock_irqsave(&stats->lock, flags);
+	list_for_each_entry_safe(node, next, &stats->list, list) {
 		if (node->pid == wq_thread->pid) {
 			node->executed++;
 			goto found;
@@ -82,17 +98,16 @@ probe_workqueue_execution(struct task_struct *wq_thread,
 	}
 	pr_debug("trace_workqueue: entry not found\n");
 found:
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
+	spin_unlock_irqrestore(&stats->lock, flags);
 }
 
 /* Creation of a cpu workqueue thread */
 static void probe_workqueue_creation(struct task_struct *wq_thread, int cpu)
 {
+	struct workqueue_global_stats *stats;
 	struct cpu_workqueue_stats *cws;
 	unsigned long flags;
 
-	WARN_ON(cpu < 0 || cpu >= num_possible_cpus());
-
 	/* Workqueues are sometimes created in atomic context */
 	cws = kzalloc(sizeof(struct cpu_workqueue_stats), GFP_ATOMIC);
 	if (!cws) {
@@ -103,27 +118,39 @@ static void probe_workqueue_creation(struct task_struct *wq_thread, int cpu)
 
 	INIT_LIST_HEAD(&cws->list);
 	cws->cpu = cpu;
-
 	cws->pid = wq_thread->pid;
 
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-	if (list_empty(&workqueue_cpu_stat(cpu)->list))
+	if (cpu == SINGLETHREAD_CPU)
+		stats = &singlethread_stat;
+	else
+		stats = workqueue_cpu_stat(cpu);
+
+
+	spin_lock_irqsave(&stats->lock, flags);
+	if (list_empty(&stats->list))
 		cws->first_entry = true;
-	list_add_tail(&cws->list, &workqueue_cpu_stat(cpu)->list);
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
+	list_add_tail(&cws->list, &stats->list);
+	spin_unlock_irqrestore(&stats->lock, flags);
 }
 
 /* Destruction of a cpu workqueue thread */
-static void probe_workqueue_destruction(struct task_struct *wq_thread)
+static void probe_workqueue_destruction(struct task_struct *wq_thread,
+					int singlethread)
 {
-	/* Workqueue only execute on one cpu */
-	int cpu = cpumask_first(&wq_thread->cpus_allowed);
 	struct cpu_workqueue_stats *node, *next;
+	struct workqueue_global_stats *stats;
 	unsigned long flags;
+	int cpu;
 
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-	list_for_each_entry_safe(node, next, &workqueue_cpu_stat(cpu)->list,
-							list) {
+	if (singlethread)
+		stats = &singlethread_stat;
+	else {
+		cpu = cpumask_first(&wq_thread->cpus_allowed);
+		stats = workqueue_cpu_stat(cpu);
+	}
+
+	spin_lock_irqsave(&stats->lock, flags);
+	list_for_each_entry_safe(node, next, &stats->list, list) {
 		if (node->pid == wq_thread->pid) {
 			list_del(&node->list);
 			kfree(node);
@@ -133,23 +160,28 @@ static void probe_workqueue_destruction(struct task_struct *wq_thread)
 
 	pr_debug("trace_workqueue: don't find workqueue to destroy\n");
 found:
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
+	spin_unlock_irqrestore(&stats->lock, flags);
 
 }
 
 static struct cpu_workqueue_stats *workqueue_stat_start_cpu(int cpu)
 {
 	unsigned long flags;
+	struct workqueue_global_stats *stats;
 	struct cpu_workqueue_stats *ret = NULL;
 
+	if (cpu == SINGLETHREAD_CPU)
+		stats = &singlethread_stat;
+	else
+		stats = workqueue_cpu_stat(cpu);
 
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
+	spin_lock_irqsave(&stats->lock, flags);
 
-	if (!list_empty(&workqueue_cpu_stat(cpu)->list))
-		ret = list_entry(workqueue_cpu_stat(cpu)->list.next,
+	if (!list_empty(&stats->list))
+		ret = list_entry(stats->list.next,
 				 struct cpu_workqueue_stats, list);
 
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
+	spin_unlock_irqrestore(&stats->lock, flags);
 
 	return ret;
 }
@@ -170,41 +202,59 @@ static void *workqueue_stat_start(void)
 static void *workqueue_stat_next(void *prev, int idx)
 {
 	struct cpu_workqueue_stats *prev_cws = prev;
+	struct workqueue_global_stats *stats;
 	int cpu = prev_cws->cpu;
 	unsigned long flags;
 	void *ret = NULL;
 
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-	if (list_is_last(&prev_cws->list, &workqueue_cpu_stat(cpu)->list)) {
-		spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
+	if (cpu == SINGLETHREAD_CPU)
+		stats = &singlethread_stat;
+	else
+		stats = workqueue_cpu_stat(cpu);
+
+	spin_lock_irqsave(&stats->lock, flags);
+	if (list_is_last(&prev_cws->list, &stats->list)) {
+		spin_unlock_irqrestore(&stats->lock, flags);
+		if (cpu == SINGLETHREAD_CPU)
+			return NULL;
 		for (++cpu ; cpu < num_possible_cpus(); cpu++) {
 			ret = workqueue_stat_start_cpu(cpu);
 			if (ret)
 				return ret;
 		}
-		return NULL;
+		/* Display singlethreaded at last */
+		return workqueue_stat_start_cpu(SINGLETHREAD_CPU);
 	}
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
+	ret = list_entry(prev_cws->list.next, struct cpu_workqueue_stats, list);
+	spin_unlock_irqrestore(&stats->lock, flags);
 
-	return list_entry(prev_cws->list.next, struct cpu_workqueue_stats,
-			  list);
+	return ret;
 }
 
 static int workqueue_stat_show(struct seq_file *s, void *p)
 {
 	struct cpu_workqueue_stats *cws = p;
+	struct workqueue_global_stats *stats;
 	unsigned long flags;
 	int cpu = cws->cpu;
 
-	seq_printf(s, "%3d %6d     %6u       %s\n", cws->cpu,
-		   atomic_read(&cws->inserted),
-		   cws->executed,
-		   trace_find_cmdline(cws->pid));
+	if (cpu == SINGLETHREAD_CPU) {
+		stats = &singlethread_stat;
+		seq_printf(s, "  * ");
+	} else {
+		stats = workqueue_cpu_stat(cpu);
+		seq_printf(s, "%3d ", cpu);
+	}
+
 
-	spin_lock_irqsave(&workqueue_cpu_stat(cpu)->lock, flags);
-	if (&cws->list == workqueue_cpu_stat(cpu)->list.next)
+	seq_printf(s, "%6d     %6u       %s\n", atomic_read(&cws->inserted),
+						cws->executed,
+					     trace_find_cmdline(cws->pid));
+
+	spin_lock_irqsave(&stats->lock, flags);
+	if (&cws->list == stats->list.next)
 		seq_printf(s, "\n");
-	spin_unlock_irqrestore(&workqueue_cpu_stat(cpu)->lock, flags);
+	spin_unlock_irqrestore(&stats->lock, flags);
 
 	return 0;
 }
@@ -265,6 +315,9 @@ int __init trace_workqueue_early_init(void)
 		INIT_LIST_HEAD(&workqueue_cpu_stat(cpu)->list);
 	}
 
+	spin_lock_init(&singlethread_stat.lock);
+	INIT_LIST_HEAD(&singlethread_stat.list);
+
 	return 0;
 
 no_creation:
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index e53ee18..936b037 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -131,7 +131,7 @@ DEFINE_TRACE(workqueue_insertion);
 static void insert_work(struct cpu_workqueue_struct *cwq,
 			struct work_struct *work, struct list_head *head)
 {
-	trace_workqueue_insertion(cwq->thread, work);
+	trace_workqueue_insertion(cwq->thread, work, cwq->wq->singlethread);
 
 	set_wq_data(work, cwq);
 	/*
@@ -291,7 +291,9 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq)
 		 */
 		struct lockdep_map lockdep_map = work->lockdep_map;
 #endif
-		trace_workqueue_execution(cwq->thread, work);
+		struct workqueue_struct *wq = cwq->wq;
+
+		trace_workqueue_execution(cwq->thread, work, wq->singlethread);
 		cwq->current_work = work;
 		list_del_init(cwq->worklist.next);
 		spin_unlock_irq(&cwq->lock);
@@ -796,7 +798,8 @@ static int create_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
 		sched_setscheduler_nocheck(p, SCHED_FIFO, &param);
 	cwq->thread = p;
 
-	trace_workqueue_creation(cwq->thread, cpu);
+	trace_workqueue_creation(cwq->thread, wq->singlethread ?
+					      SINGLETHREAD_CPU : cpu);
 
 	return 0;
 }
@@ -904,7 +907,7 @@ static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq)
 	 * checks list_empty(), and a "normal" queue_work() can't use
 	 * a dead CPU.
 	 */
-	trace_workqueue_destruction(cwq->thread);
+	trace_workqueue_destruction(cwq->thread, cwq->wq->singlethread);
 	kthread_stop(cwq->thread);
 	cwq->thread = NULL;
 }
-- 
1.6.0.4